Pulsed excitation and sampled detection fluxgate type magnetometer

ABSTRACT

A magnetic field measuring device, equipped with a fluxgate magnetometer, the device including a magnetic sensor equipped with at least one magnetic core and a plurality of windings, and configured to deliver at least one output signal, pulse generating means for emitting at least one excitation signal at the input of the magnetic sensor, in the form of a succession of excitation pulses, one excitation pulse of the excitation pulses having a duration at least 50 times less than a period of the at least one excitation signal, sampling means for sampling the output signal of the magnetic sensor, and means for, following the emission of at least one excitation pulse of the succession of excitation pulses and during the duration of the at least one excitation pulse, triggering at least one acquisition of the output signal of the magnetic sensor by the sampling means.

TECHNICAL FIELD

The present invention relates to the field of magnetometers or magneticsensors, and employs an electronic or microelectronic magnetic fielddetection or/and measuring device, comprising a fluxgate typemagnetometer magnetic sensor, as well as improved means of pulsedexcitation of the sensor and sampled detection at the output of thesensor. The invention further concerns an improved method of detectionor/and measuring by means of such a device.

The device and method according to the invention bring improvements,particularly in terms of signal to noise ratio, consumption andbandwidth.

STATE OF THE PRIOR ART

“Fluxgate” type magnetometers find use in measuring magnetic fields,which may be weak or even very weak, for example of around onemicrotesla with a resolution of around one nanotesla or even aroundseveral picoteslas, depending on the dimensions of the magnetometer.Magnetometers can be applied to the field of microelectronics and beincorporated in integrated circuits. These magnetometers are thenmanufactured by means of techniques of forming thin films.

An electronic or microelectronic device comprising a “fluxgate” typemagnetometer is conventionally equipped: with a sensor, excitation meansor an excitation circuit capable of delivering a periodic excitationsignal to the sensor, and detection means or a detection circuit at theoutput of the sensor. The sensor generally comprises a magnetic circuitor magnetic core, as well as one or several windings responsible for theexcitation of the magnetic circuit and one or several “reception” or“detection” windings responsible for the measurement. These elementsfunction in collaboration.

The excitation signal delivered to the sensor is generally sinusoidal ortriangular as in FIG. 1A. This excitation signal periodically saturatesthe magnetic circuit of the sensor, under a magnetic inductionalternately positive and negative. Due to the non-linearity of themagnetising curve of the magnetic material forming the core, the signalinduced at the terminals of the detection windings essentially comprisesodd harmonic components of the frequency of excitation (FIGS. 1B, 1C, 1Dillustrate respectively, a magnetising curve of the core, an inductioncurve in the magnetic material of the core, as well as an inducedvoltage signal). In the presence of an external magnetic field, thehysterisis cycle of the magnetic material is no longer symmetrical andone observes even harmonics of the frequency of excitation.

An example of a magnetic field measuring device according to the priorart equipped with a fluxgate magnetometer, is illustrated in FIG. 2.This device comprises a sensor 10 equipped with a magnetic circuitcomprising a magnetic core 12. Means of exciting the core 12 areprovided at the input of the magnetic circuit and comprise a currentgenerator 20 capable of delivering an excitation signal of the type ofthat illustrated in relation to FIG. 1A, the frequency f₀ of theexcitation signal being imposed by a clock circuit or a clock 22. Thecurrent generator 20 is connected to two excitation windings 13 and 14.The magnetic circuit 10 further comprises two detection windings 15 and16 wired in opposition so that the even harmonic components add to eachother and the odd harmonic components subtract from each other. From thesignal at the output of the sensor, one extracts a signal known as“useful” by means of a preamplifier and a band pass filter (blockreferenced 30 in FIG. 2) situated at the output of the two detectionwindings 15 and 16 and a synchronous detection circuit 32 situated afterthe band pass filter. The synchronous detection circuit 30 carries out adetection of the useful signal at a frequency that may be around, orequal to, 2*f₀. This frequency 2*f₀ known as “detection” frequency, maybe imposed on the synchronous detection circuit 32, through theintermediary of a phase changer 25 situated at the output of the clock22. At the output of the synchronous detection circuit 30 a low passfilter 34 may also be provided. The device may if necessary nave aslaved operating. In this case, the signal at the output of thesynchronous detection circuit serves as an error signal for a servoloop.

For a micro-fluxgate magnetometer, the wave shape, the amplitude, thefrequency, the phase between the excitation signal and the synchronousdetection are parameters independent of each other, which restricts thesuitability of the device to a single operating frequency.

With such a device as described previously, one generally observe asignificant noise in the useful signal during phases of saturation andde-saturation of the magnetic circuit 10. FIG. 3A illustrates in suchtype of device a signal 40 at the output of the sensor 10 in response toan excitation signal 42 of frequency around 200 kHz, without themagnetic circuit of the sensor being subjected to an external field. Oneobserves that the output signal 40 from the sensor 10 comprises asignificant noise 44 during the saturation and the de-saturation of themagnetic circuit. FIG. 3B illustrates, for its part, an output signal 46from the magnetic circuit 10, in response to an excitation signal 48 offrequency around 1 MHz, without the magnetic circuit 10 being subjectedto an external field. The output signal 46 also comprises a significantnoise 50.

FIG. 3C illustrates for its part signals 62, 66, at the output of thesensor 10, for a triangular excitation signal 60 of frequency around 1MHz. In the presence of an external magnetic field of +15 μT, one mayobserve in such a device, a useful signal 62 comprising positivealternations 63 then negative alternations 64 at each saturation of themagnetic circuit, twice per period of the excitation signal 60. In thepresence of a magnetic field of −15 μT, a useful signal 66 comprisingnegative alternations then positive alternations, twice per period ofthe excitation signal. The phase between the excitation signal 60 andthe synchronous detection means must be perfectly adjusted but thesensor induces a phase difference dependent on the frequency, theamplitude of excitation and the temperature. This phase problem is thereason for offsets and the phenomenon of the very low frequency noise inthe useful signal.

For a synchronous detection fluxgate magnetometer, the origin of thesignal that one detects is the non linearity of the magnetising curve ofthe magnetic material. This non-linearity shows all of the evenharmonics 69 of the excitation signal 60. For a device equipped with asynchronous detection 32 such as described previously, only the harmonicof rank 2 of the signal 70 at the output of the magnetic circuit 10 isexploited. The harmonics of superior ranks are rejected by the low passfilter 34 (FIG. 3D)

In a general manner, when a fluxgate magnetometer is combined withexcitation means delivering a triangular or sinusoidal signal, and/orcombined with a synchronous detection circuit, instabilities orphenomena of bistability appear. This default takes the form of jumps oroffsets in the signal at the output of the magnetic sensor.

The document FR 01 10853 describes a solution for reducing offsetphenomena, and in particular a method for stabilising a magnetometerequipped with a magnetic core, windings of which at least one activewinding and one receiver winding, the active winding being laid out soas to create an excitation magnetic field in the core, which sensitisesthe receiver winding, means for passing from an alternating current toan excitation frequency in the active winding and means of measuring avoltage induced at a frequency double the frequency of excitation in thereceiver winding. This method comprises at least one step consisting insubjecting the receiver winding to a supplementary alternating magneticfield.

The document “Pulse Excitation of the Micro-fluxgate Sensors”, PavelRipka and al., Oct. 12, 2000) describes for its part, a variant of amagnetic field measuring device comprising a fluxgate magnetometer aswell as a current generator delivering a square signal of cyclic ratioaround 20% at the input of the magnetic circuit of the magnetometer. Thedetection of a signal at the output of the magnetic circuit is achievedby means of a synchronous detection circuit of type “SR844 lock inamplifier” of the Stanford Research Systems company. Such a deviceenables improved performances to be obtained particularly in terms ofconsumption, but has offset shifts and very low frequency noise such asdescribed previously.

The problem is posed of finding a new electronic or microelectronicdevice comprising a fluxgate magnetometer, the performances of which areimproved in terms of signal to noise ratio, consumption and bandwidth.

DESCRIPTION OF THE INVENTION

The aim of the present invention is to describe a magnetic fieldmeasuring device equipped with at least one fluxgate magnetometer, andcomprising improved means of excitation of the sensor or magneticcircuit of the magnetometer, as well as improved means of detection ofthe signal or signals at the output of said sensor or said magneticcircuit.

The invention firstly concerns a magnetic field measuring deviceequipped with a fluxgate magnetometer, the device comprising:

-   -   a magnetic sensor equipped with at least one magnetic core and a        plurality of windings, and capable of delivering at least one        output signal,    -   pulse generating means capable of emitting at least one        excitation signal at the input of the magnetic sensor, in the        form of a succession of pulses known as “excitation” pulses,    -   means of sampling the output signal of the magnetic sensor,

the device further comprising means, for example pulse generating meansfor, following the emission of at least one given excitation pulse ofsaid succession of excitation pulses and during the duration of saidgiven excitation pulse, triggering at least one acquisition of theoutput signal of the magnetic sensor by said sampling means.

The device according to the invention may be a microelectronic device.

A “sampled” detection exploits the peak to peak amplitude of the outputsignal of the sensor and makes it possible, unlike a conventionalsynchronous detection, to exploit all the harmonics of this outputsignal.

According to one specific embodiment, the device may comprise means for:triggering at least one acquisition of the output signal of the magneticcircuit during the respective durations of each of said pulses of saidsuccession of pulses.

Such a device may if necessary comprise pulse generating means combinedwith several multiplexed magnetic sensors, the sensors each beingcombined with sampled or sampling detection means.

Such a device has an improved signal to noise ratio and consumptioncompared to devices according to the prior art, and in particularcompared to those comprising synchronous detection means at the outputof the magnetic sensor.

In a device according to the invention, the phenomena of instability orbi-stability are also reduced compared to the devices according to theprior art.

With such a device, the bandwidth is also adjustable by the frequency ofsaid excitation signal.

According to one possibility, the excitation signal may comprise or beformed of successive excitation pulses of opposite signs. This may makeit possible to limit the offset phenomena of the signal at the output ofthe sensor.

According to one possibility, which may be combined with the previouspossibility, said excitation pulses may also have equal respectivedurations or/and respective amplitudes.

According to another possibility, which may be combined with theprevious ones, said pulses may further have a rectangular shape.

The excitation signal is preferably formed of short pulses.

The sampled or sampling detection means may be controlled by at leastone control signal with two states, generated by the generating means.

According to a first embodiment, the sampling means may be provided,following said emission of said given pulse, to carry out an acquisitionof the output signal of the sensor during a given time interval lessthan the duration of said given pulse, said time interval being betweenan instant situated at a predetermined time frame, preferably not zero,after the start of said pulse and an instant situated at anotherpredetermined time frame, preferably not zero, before the end of saidgiven pulse. This may make it possible to carry out an acquisition ofthe signal at an instant when electromagnetic, capacitive or/andinductive coupling phenomena are minimised or non-existent.

According to this first embodiment, the sampling means may be furtherprovided to carry out an averaging or a smoothing out of the outputsignal of the magnetic sensor during said given time interval.

A signal known as “smoothed out” may be formed following said averagingor said smoothing out of the output signal. According to his firstembodiment, the sampling means may be capable, moreover, of memorisingsaid “smoothed out” signal, after said given time interval and up to atleast one other pulse of said succession of pulses.

According to this first embodiment, the sampling means may comprisemeans forming a switch, for example analog.

According to this first embodiment, the sampling means may furthercomprise means forming a low pass filter.

According to one embodiment, the sampling means may be provided to:following said emission of said given excitation pulse, carry out atleast one acquisition of the output signal of the sensor at a givenpredetermined instant situated after the start and before the end ofsaid given excitation pulse.

The proximity of the excitation and detection windings may lead to anelectromagnetic coupling that does not comprise a useful signal.

Said given predetermined instant may be situated in the middle of saidgiven excitation pulse. This may make it possible to carry out anacquisition of the signal at an instant when electromagnetic, capacitiveor/and inductive coupling phenomena are minimised or non-existent.

According to the second embodiment, the sampling means may be providedto carry out a memorization of the output signal of the sensor at saidgiven predetermined instant.

According to the second embodiment, the sampling means may comprise atleast one sampler-blocker.

According to one variant, the sampling means may be further capable,following the emission of a pulse, of carrying out an analog to digitalconversion of the output signal of the circuit as of or at said givenpredetermined instant. The sampling means may comprise means forming ananalog to digital converter.

According to one embodiment of the measuring device, this device iscapable of slaved operating and may comprise one or several feedbackwindings, and a feedback loop equipped with means for producing afeedback signal intended for said feedback windings.

Said means for producing a feedback signal may comprise means forming atleast one integrator.

Said means for producing a feedback signal may comprise means formemorising an information relative to the amplitude of said feedbacksignal between two excitation pulses.

According to one embodiment of the device, the means for producing afeedback signal may be controlled by at least one feedback controlsignal generated by the pulse generating means in the form of asuccession of pulses known as “feedback control” pulses.

According to this embodiment, the variations in the feedback controlsignal may be dependent on the variations in the excitation signal, thevariations in the sampling control signal themselves being dependent onthe variations in the excitation signal.

According to one possibility, the measuring device according to theinvention may further comprise: means for, following a variationaccording to a given rapidity, of the magnetic field in which themagnetic sensor is bathed, modulating the frequency of repetition ofsaid pulses of the excitation signal as a function of said givenrapidity of variation.

The invention further concerns a magnetic field measuring method bymeans of a device equipped with a fluxgate magnetometer, the devicecomprising:

-   -   a magnetic circuit or magnetic sensor, equipped with at least        one magnetic core, and capable of delivering at least one output        signal,    -   means of exciting the magnetic core, comprising generating means        capable of emitting an excitation signal at the input of the        magnetic circuit or the magnetic sensor in the form of a        succession of pulses known as “excitation” pulses,    -   means of sampling the output signal of the magnetic circuit, the        method comprising the steps consisting in:    -   emitting at least one “excitation” pulse at the input of the        sensor,    -   triggering, following said pulse, at least one acquisition of        the output signal of the magnetic sensor by the sampling means        during the duration of said pulse.

According to one specific embodiment, the method may comprise the stepsconsisting in:

-   -   emitting a succession of “excitation” pulses,    -   triggering, following each of said “excitation” pulses, at least        one acquisition of the output signal of the sensor or magnetic        circuit by the sampling means throughout the respective        durations of these “excitation” pulses.

The excitation signal may be formed of successive “excitation” pulses ofrespective opposite signs.

Said “excitation” pulses, may have equal respective durations or/andrespective amplitudes.

Said “excitation” pulses, may have a rectangular shape.

The sampling means may be controlled by at least one sampling controlsignal with two states, generated by said generating means.

According to a first embodiment of the method, said method may furthercomprise: following said emission of said “excitation” pulse, at leastone acquisition of the output signal of the sensor during a given timeinterval less than the duration of said “excitation” pulse, said timeinterval being between an instant situated at a predetermined time frameafter the start of said pulse and an instant situated at anotherpredetermined time frame before the end of said “excitation” pulse.

According to this first embodiment, the method may comprise a stepconsisting in carrying out an averaging or a smoothing out of the outputsignal of the circuit or magnetic sensor during said given timeinterval.

According to a second possibility of embodying the method, said methodmay comprise, following said emission of said “excitation” pulse, atleast one acquisition of the output signal of the sensor at a givenpredetermined instant situated after the start and before the end ofsaid “excitation” pulse, for example an instant situated in the middleof said “excitation” pulse.

According to said second embodiment possibility, the method may furthercomprise: a memorisation of the output signal of the circuit at saidpredetermined instant.

According to said second embodiment possibility, the method may furthercomprise: following the emission of a pulse, an analog to digitalconversion of the output signal of the circuit at said givenpredetermined instant.

According to one embodiment possibility, the device may furthercomprise: one or several feedback windings, and a feedback loop equippedwith means for producing a feedback signal intended for said feedbackwindings, and in which the means for producing said feedback signal arecontrolled by at least one feedback control signal generated by thepulse generating means in the form of a succession of pulses known as“feedback control” pulses, said excitation pulse emitted at the step a)of the method may have been triggered following an emission by the pulsegenerating means, of a “feedback control” pulse.

The steps a) and b) may take place during the duration of said “feedbackcontrol” pulse.

According to one embodiment possibility, the method may furthercomprise, following a variation in the magnetic field in which themagnetic sensor is bathed according to a given rapidity of variation, astep of: modulation of the frequency of repetition of said pulses of theexcitation signal as a function of the given rapidity of variation.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will be more fully understood on reading thedescription of embodiments given, purely by way of indication and innowise limitative, and by referring to the appended drawings in which:

FIGS. 1A-1D illustrate different signals representative of the operationof a magnetic field measuring device equipped with a fluxgatemagnetometer, and employed according to the prior art;

FIG. 2 illustrates an example of magnetic field measuring deviceaccording to the prior art, equipped with a fluxgate magnetometer;

FIGS. 3A-3D illustrate excitation signals emitted at the input, of afluxgate magnetometer integrated in a magnetic field measuring deviceaccording to the prior art and output signals from the magnetometer;

FIG. 4 illustrates a magnetic field measuring device according to theinvention, comprising fluxgate magnetometer type sensor, pulsedexcitation means, and improved sampling or detection means at the outputof the sensor;

FIGS. 5A and 5B, illustrate respectively:

-   -   a first example of embodiment of a magnetic field measuring        device according to the invention, comprising a fluxgate        magnetometer type sensor and improved sampling means at the        output of the sensor,    -   excitations signals from the magnetic sensor and control of said        sampling means, employed within such a device;

FIGS. 6A and 6B, illustrate respectively:

-   -   a second embodiment of a magnetic field measuring device        according to the invention comprising a fluxgate magnetometer        type sensor and improved sampling means at the output of the        sensor,    -   excitations signals from the magnetic sensor and control of said        sampling means, employed within such a device;

FIGS. 7A and 7B, illustrate respectively:

-   -   a third embodiment of a magnetic field measuring device        according to the invention comprising a fluxgate magnetometer        type sensor and improved sampling means at the output of the        sensor,    -   and excitations signals from the magnetic sensor and control of        said sampling means, employed within such a device;

FIG. 8 illustrates an example of slaved operating magnetic fieldmeasuring device according to the invention,

FIGS. 9 and 10 illustrate respectively:

-   -   another example of slaved operating magnetic field measuring        device according to the invention and equipped with means for        generating a feedback signal, said feedback signal being        delivered by means controlled by a “pulsed” control signal,    -   a chronogram of the operation of this example of device;

FIG. 11 illustrates another example of slaved operating magnetic fieldmeasuring device according to the invention and equipped with means tomodulate the frequency of repetition of the pulses emitted towards themagnetic circuit as a function of the rate of variation in the magneticfield in which the magnetic sensor is bathed;

FIG. 12 illustrates measurement signals obtained by means of an exampleof device employed according to the invention.

Identical, similar or equivalent parts of the different figures bear thesame numerical references so as to facilitate passing from one figure tothe next.

The different parts represented in the figures are not necessarilyrepresented according to a uniform scale, in order to make the figuresmore legible.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

An example of electronic detection or/and measuring device according tothe invention, comprising a magnetometer type sensor 100, is illustratedin FIG. 4. The sensor 100 may be in particular a fluxgate, ormicrofluxgate or integrated fluxgate sensor, in other words a fluxgatemagnetometer included in a microelectronic device such as a MEMS (MEMSfor micro electromechanical system) or a chip. The electronic detectiondevice further comprises means of excitation or an excitation circuit atthe input of the sensor 100, and detection means or a detection circuitat the output of the sensor 100. The magnetic sensor is formed of amagnetic circuit 101 equipped with a magnetic core 102. The magneticcircuit 101 may have a high magnetic permeability, for example between500 and 2000, for a magnetic core based on Iron/Nickel. The magneticcore 102 may be closed. The invention may also apply to magnetic coreshaving other shapes to that illustrated in FIG. 4, and if necessary to amagnetic circuit comprising an open core. In the case of amicro-fluxgate or integrated fluxgate, the magnetic circuit may forexample have a thickness of around one or several micrometers.

One or several excitation windings are provided to saturate the magneticcore 102. The device may comprise for example a first excitation winding104 and a second excitation winding 106, connected in series and woundaround branches of the core 102. The excitation windings 104 and 106 arearranged so as to create an excitation magnetic field in the magneticcore 102. The device may comprise a first and a second detection windingnoted respectively 108 and 110 also each wound around the core 102 ofthe magnetic circuit. The magnetic core 102 may be orientated forexample according to the axis known as “easy magnetisation” or along theaxis known as “difficult magnetisation”.

The number of detection and excitation windings of the magnetometeraccording to the invention, as well as the layout of these windings isin no way restricted to that which is illustrated in FIG. 4. Accordingto a variant embodiment of the device, the core of the magnetic circuitmay be formed of several distinct or/and disjointed branches, forexample of two branches each comprising an excitation winding and adetection winding. This variant may enable the windings to be connectedaccording to a differential assembly, and thereby limit or eliminate theelectromagnetic, inductive or/and capacitive couplings, between theexcitation and detection windings. According to another variant, themagnetic circuit may be formed of a branch equipped with a winding, saidwinding being wired to a Wheatstone bridge comprising for example threefixed impedances, one of said impedances having the same value as thewinding when the magnetic circuit is not saturated.

A pulse generator or pulse generating means 120 are provided at theinput of the magnetic circuit 101, and connected for example to an endof the first excitation winding 104 and to an end of the secondexcitation winding 106. The pulse generator 120 is provided to deliveran excitation signal S₁ that may be in the form of a succession of shortpulses of current known as “excitation” pulses, emitted at the input ofthe windings 104 and 106, and if necessary periodic. The pulses of theexcitation signal S₁ have an amplitude chosen in such a way as tosaturate the magnetic circuit 101 of the sensor 100. “Short pulses” istaken to mean pulses in which the duration or the width T₁ is very shortcompared to the period of the excitation signal, for example at least 50times less than the period T of the excitation signal or at least 50000times less than the period of the excitation signal. The pulse generator120 is employed to generate pulses of a duration or width T₁, providedsufficiently big so that a signal noted S₂ at the output of the sensor,may be exploited by the detection means.

The pulses of the excitation signal S₁ may have for example a durationor a width at least greater than 10 nanoseconds or/and at least lessthan 30 nanoseconds. The pulses of the excitation signal S₁ may have aduration or a width chosen preferably between 10 and 30 nanosecondsparticularly for a sensor in which the thickness of the core or themagnetic circuit is around 1 μm to several micrometers and the length ofwhich is around 100 μm to several hundreds of micrometers. This timeinterval is chosen as a function of the time constant of the circuit.

For a frequency of pulses of the excitation signal S₁ around 50 kHz, theduration of the pulses may be chosen for example one hundred timessmaller than the period of the excitation signal, for example around 20nanoseconds. The current consumed may thereby be 100 times less than theamplitude of the pulse.

The pulses of the excitation signal S₁ may have a rectangular orsubstantially rectangular shape. “Substantially” rectangular shape istaken to mean the pulses comprise fronts of duration for example around2 nanoseconds, or for example between 1 nanosecond and 5 nanoseconds.

Compared to triangular or sinusoidal signals employed in devicesaccording to the prior art, the excitation signal S₁ formed of asuccession of pulses makes it possible in particular to obtain a reducedconsumption. The cyclic ratio and the frequency of the excitation signalS₁ generated by the means 120, may be modulated, for example in a ratiofrom 1 to 10000. Means for modulating the frequency of the excitationsignal may be provided.

The frequency of the excitation signal S₁ may be for example between 100Hz and 1 MHz and chosen as a function of the type of detection that thesensor 100 is intended to carry out.

A low excitation frequency, for example between 100 Hz and 1 kHz, may bechosen for example for applications of the sensor that require a lowconsumption, for example at least inferior to 100 μA under an excitationvoltage of amplitude for example around 3 volts, but do not necessitatea significant bandwidth, for example of around or less than 1/10 of thefrequency of the excitation signal, i.e. between 10 Hz and 100 Hz.

An excitation frequency between 50 kHz and 500 kHz may be chosen forexample for applications that require a bandwidth of around or at least10 kHz as well as a noise no higher than 5 nT/Hz^(1/2).

According to one possibility, the excitation signal S₁ may be in theform of an alternation of positive pulses 125 and negative pulses 126 orbe formed of at least two successive pulses of opposite signs. In thisway, the useful component of the signal S₂ at the output of the sensor100 has a sign independent of that of the pulses emitted at the input ofthe sensor 100, whereas any parasitic couplings between the excitationand detection windings cancel each other out. The negative pulses 126and positive pulses 125 may have equal respective widths T₁ or/andrespective amplitudes A. Said positive 125 and negative 126 pulses maythus be symmetrical. An excitation signal S₁ employed with symmetricpulses can make it possible to reduce or eliminate offsets in the signalS₂ at the output of the magnetic sensor.

According to one possibility, the excitation signal S₁ may be employedfor a square or rectangular signal to which one has applied a high passfiltering. The excitation signal S₁ may if necessary be employed by aCMOS (complementary metal oxide semiconductor) circuit.

Sampling means 130 are provided, to carry out, in particular,acquisitions of the signal S₂ at the output of the sensor 100, as afunction of a sampling control signal S₃ and in particular variations ina sampling control signal S₃ or the state of a sampling control signalS₃ delivered at the input of the sampling means 130. The variations inthe control signal S₃ are themselves dependent, or the state of thecontrol signal S₃ is itself dependent, on variations in the excitationsignal S₁.

Means are employed, following the emission or the production of a pulsein the excitation signal S₁, to modify at least once the samplingcontrol signal S₃ or the state of the sampling control signal S₃, so asto trigger at least one acquisition of the output signal S₂ of thesensor 100 during the duration of this excitation pulse. In other words,the measuring device is provided so that the sampling means 130 carryout an acquisition of the signal S₂ at the output of the sensor or themagnetic circuit at instants situated during the respective durations ofthe pulses of the excitation signal S₁. According to a specificembodiment, means may be employed to trigger at least one acquisition ofthe signal at the output of the sensor or the magnetic circuit,following each of the excitation pulses emitted, during the respectivedurations of these pulses. The sampling control signal S₃ may be formedand delivered by the pulse generating means 120. The sampling controlsignal S₃ may be for example a signal with two states, as illustrated inFIG. 4.

The sampling means 130 produce at the output a signal S₄ representativeof a measured magnetic field. The signal S₄ at the output of thesampling means may be for example an analog voltage or, if necessary, adigital signal, for example a numeric word. The sampling means 130 maycomprise for example means forming a sampler-blocker. According to avariant, the sampling means 130 may comprise means forming ananalog-digital converter.

At the output of the sampling means 130, a stage 140 comprising means oflow pass filtering and/or means of low frequency amplification may beprovided. This stage 140 delivers an output signal S₅.

With such a device, one obtains a signal S₂ at the output of the highamplitude sensor, for example around 30 mV for a magnetic field to bemeasured of around 30 μT, which makes it possible to protect against anamplifier between the output of the magnetic sensor and the samplingmeans 130, and in particular a high frequency amplifier. The employmentof low frequency amplification means after the sampling means 130,rather than a high frequency amplifier before the sampling means 130,may make it possible in particular to reduce the consumption of themeasuring device.

A variant of the electronic detection or/and measuring device accordingto the invention previously described, equipped with a fluxgatemagnetometer type sensor 210 is illustrated in FIG. 5A.

Generating means 220 deliver an excitation signal S₁₀ to a sensor ormagnetic circuit 210. The excitation signal S₁₀ may be of the type ofthat S₁ described previously. At the output of the sensor or magneticcircuit 210, are provided sampling means 230 capable of carrying out, atleast one acquisition of a signal S₂₀ at the output of the sensor 210during each of the pulses of the excitation signal S₁₀. According tothis variant, the sampling means 230 may be equipped with means forminga switch, for example an analog switch 232, the opening and the closingof which are controlled by a sampling control signal S₃₁ also generatedby the excitation signal S₁₀ generating means 220. The variations in thecontrol signal S₃₁ are dependent on those of the excitation signal S₁₀.The sampling means 230 further comprise means forming a low pass filter234. The means forming a low pass filter 234 may be in the form forexample of means forming a resistor 235 combined with means forming acapacitor 236. An amplifier 241 may be provided at the output of thefilter 234. The amplifier 241 is equipped with a high input impedance,for example greater than 10 MΩ, so as to conserve a constant signal atthe output of the sampling means 230, when the switch 232 is open. Thetime constant of the capacitor 236 and the input resistance of theamplifier is preferably much greater than the largest period of theexcitation pulses, for example between 5 and 10 times greater.

The amplifier 241 may be for example arranged according to a followerassembly. The sampling means 230 deliver a signal representative of themagnetic field to be measured, for example in the form of an analogvoltage.

In FIG. 5B, are illustrated curves representative respectively, of thesampling control signal S₃₁ for example in the form of a signal with twostates, and the excitation signal S₁₀ emitted at the input of the sensor210. The excitation signal S₁₀ is formed of a succession of pulses 225,226, alternatively of opposite signs, for example positive thennegative. Following the emission or the production of a first pulse 225in the excitation signal S₁ at an instant t₁, the sampling controlsignal S₃₁ is modified or caused to change state, after a predeterminedtime interval θ₁ or a predetermined time or time frame θ₁ and passesfrom a first state to a second state, for example from the low state tothe high state (portion referenced 227 a in FIG. 5B), so as to close theswitch 232 and trigger an acquisition of the signal at the output of thesensor by the sampling means 230. For this embodiment variant, theacquisition of the signal S₂₀ at the output of the sensor 210 is carriedout for the duration of the first excitation pulse, a predetermined timeframe θ₁ after the start of this first pulse. In this way, one does notcarry out detection at the moment when the excitation pulse 225 isemitted or at the start of this excitation pulse 225, in other words ata moment during which electromagnetic parasite electromagnetic couplingor noise phenomena in the signal S₂₀ are likely to arise.

The control signal S₃₁ is maintained in the second state for apredetermined duration between an instant t₂ and an instant t₃ (portionreferenced 227 b in FIG. 5B), so as to maintain the switch closed forthis predetermined duration. In other words, the acquisition of thesignal at the output of the sensor carried out for the duration of thefirst excitation pulse 225, is carried out between the instant t₂ andthe instant t₃. Then, a predetermined time or a time frame θ₂ before theend of the first excitation pulse 225, the sampling control signal S₃₁is modified or caused to chance state, and passes from the second stateto the first state, for example from the high state to the low state(portion referenced 227 c in FIG. 5B), so as to open the switch 232. Anaveraging or smoothing out of the voltage induced at the output of thesensor 210 is also carried out during said duration of the pulse 225,between the instant t₂ and the instant t₃. The duration of the firstpulse 225 ends at an instant t₄. The change of state of the controlsignal, provided at a time frame θ₂ before t₄, makes it possible not tocarry out a detection at the moment when the pulse 225 ends or at theend of the excitation pulse 225, in other words at a moment during whichparasite coupling or noise phenomena in the signal S₃₀ can arise. Asignal known as “smoothed out” is formed by smoothing out of the outputsignal S₂₀ of the sensor 210.

Then, a second pulse 226 for example of negative sign is emitted. Thecontrol signal S₃₁ is modified or caused to change state (portionreferenced 227 d), a predetermined time frame θ₁ after the start of thesecond pulse. Then, a predetermined time frame θ₂ before the end of thesecond pulse 226, the sampling control signal S₂₁ is modified or causedto change state, and passes from the second state to the first state,for example from the high state to the low state, so as to open theswitch 232.

Between the pulses 225 and 226 the switch is now open, and the smoothedout signal at the output of the sampling means 230 is memorised. Thesampling means 230 are provided to memorise said “smoothed out” signal,up to the second excitation pulse 226.

A second variant of electronic detection or/and measuring deviceaccording to the invention equipped with a fluxgate magnetometer typesensor 210, is illustrated in FIG. 6A. According to this variant, at thecutout of the sensor or magnetic circuit 210, are provided samplingmeans equipped with a sampler-blocker 330. The sampler-blocker 330delivers a signal representative of the magnetic field to be measured,for example in the form of a voltage. Generating means 320 deliver anexcitation signal S₁₀, to the magnetic sensor 210. At the output of thesensor 210, the sampling means 330 are employed to carry out, followinga pulse of the excitation signal S₁₀, an acquisition of a signal S₂₀ atthe output of the sensor 210 for the duration of this pulse. Accordingto this variant, the sampling means 330 are controlled by a samplingcontrol signal S₃₂ generated by the means 320 for generating theexcitation signal S₁₀. The variations in the control signal S₃₂ aredependent on those of the excitation signal S₁₀.

In FIG. 6B are illustrated curves representative respectively, of thesampling control signal S₃₂, for example in the form of a signal withtwo states, emitted at the input of the sampler-blocker 330 and theexcitation signal S₁₀, for example in the form of a current, emitted atthe input of the sensor 210. The excitation signal S₁₀ is formed of asuccession of pulses 225, 226, alternatively positive then negative.Following the emission or the production of a first pulse 225 in theexcitation signal S₁₀ at an instant t′₁, the sampling control signal S₃₂is caused to change state and passes from a first state to a secondstate, for example from the low state to the high state, at an instantt′₂ situated during the duration of the pulse 225. The pulse generatingmeans 320 are, in this example, employed so that the instant t′₂ ofchange of state of the control signal S₃₂ is situated in the middle ofthe excitation pulse 225. The change of state of the control signal S₂₂at the instant t′₂ provokes an acquisition, by the sampler-blocker 330,of the signal at the output of the sensor. At the instant t′₂, thesampler-blocker 330 memorises the signal at the output of the sensor.Carrying out an acquisition of the signal S₂₀, at an instant situatedfor example in the middle of the pulse 225, may make it possible toobtain a signal that does not include parasite noise due toelectromagnetic coupling phenomena during transitions or changes ofstates of the excitation signal.

A third variant of electronic detection or/and measuring deviceaccording to the invention, equipped with a fluxgate magnetometer typesensor 210, is illustrated in FIG. 7A. According to this variant, at theoutput of the sensor or magnetic circuit 210, are provided samplingmeans comprising an analog to digital converter 430. The converter 430delivers a signal representative of the magnetic field to be measured,for example in the form of a numeric word.

In FIG. 7B are illustrated curves representative respectively, of asampling control signal S₃₃ for example in the form of a signal with twostates, emitted at the input of the converter 430 and an excitationsignal S₁₀, as described previously, emitted at the input of the sensor210. The excitation signal S₁₀ is formed of a succession of pulses 225,226, alternately positive then negative. Following the emission or theproduction of a first pulse 225 in the excitation signal S₁₀ at aninstant t″₁, the sampling control signal S₃₃ passes from a first stateto a second state, for example from the low state to the high state, atan instant t″₂ situated during the duration of the pulse 225 between theinstant t″₁ and an instant t″₃ referenced in FIG. 7B, the instant t″₂ ofchance of state of the control signal S₃₃ may be provided to be situatedin the middle of the excitation pulse 225. The change of state of thecontrol signal S₃₃ at the instant t″₂ provokes in particular anacquisition, by the converter 430, of the signal S₂₀ at the output ofthe sensor 210, as well as a conversion of this signal. Carrying out aconversion of the signal S₂₀, at an instant situated in the middle ofthe pulse 225, may make it possible to obtain a signal in which noiseparasite phenomena due in particular to coupling during transitions orchanges of states of the excitation signal, are minimised.

A variant of the example of electronic detection or/and measuring deviceaccording to the invention given previously in relation to FIG. 4, isillustrated in FIG. 8. For this variant, the measuring device is capableof having a slaved operating and comprises a servo or feedback loop. Asignal representative of a measured magnetic field, for example theoutput signal S₅ of the amplifier 140 or (according to one possibilitynot represented) the numeric word at the output of an analog to digitalconverter (such as the converter referenced 430 in FIG. 7A) plays therole of an error signal of the servo loop. This error signal is appliedat the input of the means forming an integrator 560, for example anamplifier integrator or a digital integrator. At the output of theintegrator 560 a signal S₆ known as “feedback” signal, intended to feedone or several feedback windings is delivered. The “feedback” windingsmay be, one or several excitation windings 104, 106 or one or severalspecific supplementary windings (not represented). The application of afeedback signal S₆ to the feedback windings makes it possible to form afeedback magnetic field that opposes the magnetic field in which thesensor 100 is bathed. In this example, the magnetic sensor 100 operatesunder a magnetic field, the average value of which is zero. Themeasuring dynamic and the linearity of the measuring device may therebybe improved.

A specific embodiment of the slaved operating magnetic field measuringdevice and with feedback known as “pulsed”, is illustrated in FIG. 9. Inthis example, means for applying a feedback signal S₈ to the magneticsensor 100, are controlled by a feedback control signal S₇ formed of asuccession of pulses. The device thus moreover comprises, control means670 capable of delivering the feedback signal S₈, and controlled by thefeedback control signal S₇. This feedback control signal S₇, may be forexample a logic signal, delivered by the pulse generator 120. In thisexample, the feedback loop comprises means 660 forming at least oneintegrator, situated at the output of the amplifier and filtering stage140. Means for memorising an information relative to the amplitude ofthe feedback signal between two excitation pulses may also be provided.According to one possible embodiment, these memorisation means maybelong to the integrator 660. The feedback control means 670 receive atthe input the output signal S₆₁ of the integrator 660 and are capable,as a function of the state of the feedback control signal S₇, to emit ornot, a feedback signal S₈, the amplitude of which depends on that of theoutput signal S₆₁.

An operation of the pulsed feedback device is now going to be given inrelation to the chronogram of FIG. 10, in which curves representative ofa feedback control signal S₇, an excitation signal S₁, and a samplingcontrol signal S₃ are given. The signals S₁, S₃, S₇ may be formed by thepulse generator 120 and formed respectively, of a first succession ofpulses 723, 724 of a second succession of pulses 725; 726, and of athird succession of pulses 728, 729. The variations in the excitationsignal S₁, are dependent on those of the feedback control signal S₇,whereas the variations in the sampling control signal S₃ are dependanton those of the excitation signal S₁.

As of an instant t₀, the feedback control signal S₇ changes state. Afeedback signal S₈ (not represented in this figure), the amplitude ofwhich has been defined and memorised by the integrator 660 during aprevious sampling, is then applied to the feedback windings of thesensor 100 as of the instant t₀.

Then, after a predetermined time frame θ₀, an excitation pulse 725 isemitted at an instant t₁. The predetermined time frame θ₀ is provided soas to enable the establishment of a feedback magnetic field at a precisevalue, and may be for example such that θ₀=5τ where τ is the timeconstant of the magnetic circuit of the sensor 100.

Then, a predetermined time frame θ₁ after the instant t₁, the outputsignal S₂ of the detection windings 108, 110, is sampled by the samplingmeans 130, amplified by the means 140 and applied at the input of theintegrator 660. The integrator 660 corrects if necessary the feedbacksignal in order to tend to cancel the output signal S₂ from thedetection windings 108, 110. A new value of the feedback signal ismemorised up to the following sample.

Then, the sampling of the output signal S₂ of the detection windings isinterrupted at an instant t₃. The excitation pulse then ends at aninstant t₄, a predetermined time frame θ₂ after the instant t₃. Thefeedback control pulse then ends at an instant t₅. As of the instant t₅and up to a following sample, the feedback is stopped.

After several samples enabling the stabilisation of the servo loop, thevalue of the feedback signal memorised is the image of the magneticfield in which the magnetic sensor is bathed and that one wishes tomeasure.

In this example of embodiment, the pulses 728, 729 of the samplingcontrol signal S₃ are situated respectively during the respectivedurations of the pulses of the excitation signal S₁, the excitationpulses 725, 726 being themselves respectively situated during thedurations of the pulses 723, 724, of the feedback control signal S₇.

A variant of the previous example of device, with slaved operating, willnow be given in relation to figure 11. For this variant, the device hasan operation known as “self-adapting”. “Self-adapting” is taken to meanthat the frequency of repetition of the excitation pulses emitted by thegenerating means 120 may be adjusted in an automatic manner within thedevice, as a function of the rate or rapidity of variation in themagnetic field to be measured surrounding the sensor 100. In thisembodiment, means are thus employed to modulate the frequency ofrepetition of the excitation pulses of the signal S₁ delivered by thegenerating means 120, as a function of the rate of variation or rapidityof variation in the magnetic field to be measured surrounding the sensor100. These modulation means may comprise for example means 682 forming adifferentiator, connected to an output of the integrator 660, means 684forming a rectifier without threshold, connected to an output of themeans forming a differentiator 682, as well as means 686 forming avoltage controlled oscillator, connected to an output of the meansforming a rectifier 684, the means 686 forming an oscillator beingconnected to the pulse generating means 120.

Such a device may be provided for example so that, when the surroundingmagnetic field is constant or varies slowly, the frequency of repetitionof the excitation pulses is low, whereas when the magnetic field variesrapidly, the frequency of repetition of the excitation pulses is high.Such a mode of operation may enable the consumption to be optimised.

A compass device comprising such a type of self-adapting and slavedoperating magnetic field measuring device, may be employed according tothe invention and provided for example so that the frequency of themagnetic field measurements varies according to whether the compass isimmobile or in movement.

The operation of the compass device employed according to the inventionmay be as follows: when the sensor 100 is immobile, the magnetic fieldto be measured is constant or substantially constant and the outputsignal is also constant. The signal at the output of the differentiator682 is then zero, the signal at the output of the rectifier withoutthreshold 684 is zero and the frequency of repetition of the excitationpulses is minimal, for example around 100 Hz. When the sensor 100 isbrought into movement, the magnetic field is variable, and the outputsignal is also variable. The signal at the output of the differentiator682 is then not zero, whereas the signal at the output of the rectifierwithout threshold 684 is positive and the frequency of repetition of theexcitation pulses is high, for example around 100 kHz. Thus, thebandwidth is low when the magnetic field varies little, and high whenthe magnetic field varies rapidly. Such a compass device, may beequipped with two sensors of the type of sensor 100, positioned at 90°,and employed so that the direction of north is calculated as a functionof the output signal S₄ of each of these two sensors.

FIG. 12 illustrates measuring signals 810 a and 810 b known as “usefulsignals” obtained by means of the devices previously described and inresponse to respectively a first excitation pulse 820 a and a secondexcitation pulse stemming from the pulse generating means 120, and showsthat a “sampled” detection employed according to the invention mayenable the peak to peak amplitude of the measuring signal to beexploited.

1. A magnetic field measuring device, equipped with a fluxgatemagnetometer, the device comprising: a magnetic sensor equipped with atleast one magnetic core and a plurality of windings, and configured todeliver at least one output signal; pulse generating means for emittingat least one excitation signal at the input of the magnetic sensor, inthe form of a succession of excitation pulses, one excitation pulse ofsaid excitation pulses having a duration at least 50 times less than aperiod of said at least one excitation signal; sampling means forsampling the output signal of the magnetic sensor; and means for,following the emission of at least one excitation pulse of saidsuccession of excitation pulses and during the duration of said at leastone excitation pulse, triggering at least one acquisition of the outputsignal of the magnetic sensor by said sampling means.
 2. The deviceaccording to claim 1, the excitation signal formed of successiveexcitation pulses of opposite signs.
 3. The device according to claim 1or 2, said excitation pulses having equal respective durations or/andrespective amplitudes.
 4. The device according to claim 3, saidexcitation pulses having a rectangular shape.
 5. The device according toclaim 1, in which the sampling means are controlled by at least onesampling control signal with two states, generated by the pulsegenerating means.
 6. The device according to claim 1, the sampling meansconfigured to, following said emission of said excitation pulse, carryout at least one acquisition of the signal at the output of the magneticsensor during a given time interval less than the duration of saidexcitation pulse, said time interval between an instant situated at afirst predetermined time frame after, the start of said excitation pulseand an instant situated at a second predetermined time frame before theend of said excitation pulse.
 7. The device according to claim 6, thesampling means configured to carry out an averaging or a smoothing outof the output signal of the magnetic sensor during said given timeinterval.
 8. The device according to claim 7, in which a smoothed outsignal is formed following said averaging or said smoothing out of saidoutput signal, the sampling means configured to memorize said smoothedout signal, after said given time interval and up to at least one otherexcitation pulse of said succession of excitation pulses.
 9. The deviceaccording to claim 6, the sampling means further comprising means forforming an analog switch.
 10. The device according to claim 9, thesampling means further comprising means for forming a low pass filter.11. The device according to claim 1, the sampling means configured,following said emission of said excitation pulse, to carry out at leastone acquisition of the output signal of the sensor at a givenpredetermined instant situated after the start and before the end ofsaid excitation pulse.
 12. The device according to claim 11, said givenpredetermined instant situated in the middle of said excitation pulse.13. The device according to claim 11, the sampling means configured tocarry out a memorisation of the output signal of the sensor at saidgiven predetermined instant.
 14. The device according to claim 11, thesampling means further comprising at least one sampler-blocker.
 15. Thedevice according to claim 12 or 13, the sampling means configured tocarry out an analog to digital conversion of the output signal of thesensor at said given predetermined instant.
 16. The device according toclaim 1, in which the device is configured to adopt a slaved operatingand further comprises one or several feedback windings, and a feedbackloop equipped with means for producing a feedback signal intended forsaid feedback windings.
 17. The device according to claim 16, said meansfor producing a feedback signal further comprising means for forming atleast one integrator.
 18. The device according to claim 16 or 17, saidmeans for producing a feedback signal further comprising means formemorising an information relative to the amplitude of said feedbacksignal, between two excitation pulses.
 19. The device according to claim16, in which the means for producing a feedback signal are controlled byat least one feedback control signal generated by the pulse generatingmeans in the form of a succession of feedback control pulses.
 20. Thedevice according to claim 1, in which said magnetic sensor is bathed ina magnetic field, the device further comprising: means for, following avariation in the magnetic field according to a given rapidity in whichthe magnetic sensor is bathed, modulating the frequency of repetition ofsaid pulses of the excitation signal as a function of said givenrapidity.
 21. A magnetic field measuring method using a device equippedwith a fluxgate magnetometer, the device including: a magnetic sensor,equipped with at least one magnetic core and a plurality of windings,and configured to deliver at least one output signal, means for excitingthe magnetic core, including pulse generating means configured to emitat least one excitation signal at the input of the magnetic sensor inthe form of a succession of excitation pulses, one excitation pulse ofsaid excitation pulses having a duration at least 50 times less than aperiod of said excitation signal, and sampling means for sampling theoutput signal of the magnetic sensor, the method comprising: a) emittingat least one excitation pulse at the input of the magnetic sensor; andb) triggering, following said emission of said excitation pulse, atleast one acquisition of the output signal of the magnetic sensor by thesampling means during the duration of said excitation pulse.
 22. Themethod according to claim 21, the excitation signal formed of severalsuccessive excitation pulses of respective opposite signs.
 23. Themethod according to claim 21 or 22, said excitation pulses having equalrespective durations or/and respective amplitudes.
 24. The methodaccording to claim 23, said excitation pulses having a rectangularshape.
 25. The method according to claim 21, in which the sampling meansare controlled by at least one control signal with two states, generatedby the pulse generating means.
 26. The method according to claim 21,further comprising: acquiring, following said emission of saidexcitation pulse, at least once, the output signal of the sensor duringa given time interval less than the duration of said excitation pulse,said time interval between an instant situated at a first predeterminedtime frame after the start of said pulse and an instant situated at asecond predetermined time frame before the end of said given pulse. 27.The method according to claim 26, further comprising: carrying out anaveraging or a smoothing out of the output signal of the magnetic sensorduring said given time interval.
 28. The method according to claim 27,in which a smoothed out signal is formed following said averaging orsaid smoothing out of the output signal, the sampling means configuredto memorize said smoothed out signal, after said given time interval andup to at least one other excitation pulse of said succession ofexcitation pulses.
 29. The method according to claim 21, furthercomprising: acquiring, following said emission of said excitation pulse,at least once, the output signal of the sensor at a given predeterminedinstant situated after the start and before the end of said excitationpulse.
 30. The method according to claim 29, said given predeterminedinstant situated in the middle of said excitation pulse.
 31. The methodaccording to claim 29 or 30, further comprising: memorizing the outputsignal of the sensor at said given predetermined instant.
 32. The methodaccording to claim 29 or 30, further comprising: converting the outputsignal of the sensor from analog to digital at said given predeterminedinstant.
 33. The method according to claim 21, in which the devicefurther comprises: one or several feedback windings, and a feedback loopequipped with means for producing a feedback signal intended for saidfeedback windings, the means for producing said feedback signal arecontrolled by at least one feedback control signal generated by thepulse generating means in the form of a succession of feedback controlpulses, said excitation pulse emitted at the step a) triggered followingan emission by the pulse generating means of a feedback control pulse.34. The method according to claim 33, a) and b) taking place during theduration of said feedback control pulse.
 35. The method according toclaim 21, further comprising: modulating, following a variationaccording to a given rapidity of variation in the magnetic field inwhich the magnetic sensor is bathed, the frequency of repetition of saidexcitation pulses of the excitation signal as a function of the givenrapidity of variation.